Functional interaction between the Arabidopsis orthologs of spindle assembly checkpoint proteins MAD1 and MAD2 and the nucleoporin NUA

Abstract

In eukaryotes, the spindle assembly checkpoint (SAC) ensures the fidelity of chromosome segregation through monitoring the bipolar attachment of microtubules to kinetochores. Recently, the SAC components Mitotic Arrest Deficient 1 and 2 (MAD1 and MAD2) were found to associate with the nuclear pore complex (NPC) during interphase and to require certain nucleoporins, such as Tpr in animal cells, to properly localize to kinetochores. In plants, the SAC components MAD2, BUR1, BUB3 and Mps1 have been identified, but their connection to the nuclear pore has not been explored. Here, we show that AtMAD1 and AtMAD2 are associated with the nuclear envelope during interphase, requiring the Arabidopsis homolog of Tpr, NUA. Both NUA and AtMAD2 loss-of-function mutants have a shorter primary root and a smaller root meristem, and this defect can be partially rescued by sucrose. Mild AtMAD2 over-expressors exhibit a longer primary root, and an extended root meristem. In BY-2 cells, AtMAD2 is associated with kinetochores during prophase and prometaphase, but not metaphase, anaphase and telophase. Protein-interaction assays demonstrate binding of AtMAD2 to AtMAD1 and AtMAD1 to NUA. Together, these data suggest that NUA scaffolds AtMAD1 and AtMAD2 at the nuclear pore to form a functional complex and that both NUA and AtMAD2 suppress premature exit from cell division at the Arabidopsis root meristem.

GAP Activity, but Not Subcellular Targeting, Is Required for Arabidopsis RanGAP Cellular and Developmental Functions

“…For instance, Rae1, an mRNA export factor associated with the nuclear pore complex, is also involved in spindle formation and chromosome segregation (Lee et al, 2009). Similarly, NUA (the Arabidopsis homolog of Tpr/Mlp1/Mlp2/Megator) (Jacob et al, 2007;Xu et al, 2007) is a nuclear pore complex protein, which is a part of a spindle assembly checkpoint (Ding et al, 2012). Further work is required to shed more light on these developmental functions of RanGAP1 and to determine other molecular players involved in these processes alongside RanGAP.…”

Endopolyploidization and flowering time are antagonistically regulated by checkpoint component MAD1 and immunity modulator MOS1

“…The association of SAC with MOS1 prompted us to analyse the role of SAC components in flowering time control. A mad2-2 mutant (SAIL_191_G06) 7 , and two mad1 mutants, mad1-1 (Salk_039008) and mad1-2 (Salk_073889), were isolated from the T-DNA insertion collection 24,25 ( Supplementary Fig. 4a,b).…”

“…In Arabidopsis, the homologues of SAC components including MAD1, MAD2, BUB3.1 and BUBR1 have been identified. Physical interactions among Arabidopsis MAD1, MAD2, BUB3.1 and BUBR1 were revealed by yeast twohybrid (Y2H) and/or bimolecular fluorescence complementation (BiFC) assays, and the dynamics of their localization at kinetochore during the cell division suggest that they may have a SAC function [6][7][8] . However, the petal-specific knockdown of MAD2 and BUBR1 in Arabidopsis did not cause any defects in mitosis, although they resulted in reduced petal growth 9 .…”

“…However, the petal-specific knockdown of MAD2 and BUBR1 in Arabidopsis did not cause any defects in mitosis, although they resulted in reduced petal growth 9 . The loss-of-function (l-o-f) mutant mad2-2 did not exhibit any defects except for an arrested root growth 7 . Therefore, the biological function of plant SAC homologues is still unclear.…”

Discovering the World of Plant Nuclear Proteins

“…NUA forms a complex with Arabidopsis MAD1 and MAD2 (mitotic arrest deficient 1 and 2) proteins (Ding et al 2012) and plays a role in spindle checkpoint activation during mitosis.…”